A broken spirit is a broken horse, one that may never, ever be repaired no matter how much love you patch them with.
A horses spirit should be tamed, yes, but never broken.
I see a horses spirit in the terms of fire.
My gelding Loki has a strong one, a hot blaze, he is hard mouthed, hard headed, and difficult in the saddle. If that blaze were to be tamed, contained, he would make a fantastic show horse and trail companion. Tamed, not crushed.
Red Man has a changing flame, from soft and mellow to blazing hot. He is very free-minded, he does not like to be contained or constrained in anyway. He is difficult to tame as he is changing, care must be taken not to suffocate the fire that makes him what he is. Like his brother, he too would excell both in the ring and on the trails.
Sammy has a mellow, relaxing flame. It is warming, gentle, but not hot or uncontrollably changing like Loki or Red's. It is that what makes him so wonderful to be around. If it were estinguished...nothing would be left.
I would never in my life entrust any of my horses to someone who 'breaks their spirits'. I would rather have them sit in the pasture and become fat and useless.